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Problem with audio drift
I’ve appreciated this forum over the past couple of years as my audio business has lead me into shooting video of music concerts, recitals and audition recordings.
I have a Sound Device 702 that I record audio with and a Panasonic HDC-TM700 that I record video with. I merge the wav files from the SD702 with the AVCHD files from the TM700 in Vega Home Studio Platinum 10. My work process includes copying the wav files and the AVCHD files onto an external hard drive (7200 rpm, e-sata) and manually syncing the audio from each take. Recently I noticed that the audio had drifted from the video (about 13 minutes into a Beethoven sonata) while watching a rendered file.
The ‘Video Guys’ suggested that the hard drive, over 50% full could be the problem. They suggested adding a raid drive and if that didn’t fix things upgrade to Vegas Pro.
I’ve also been considering a Sound Device PIX. I think the PIX would save two steps in the work process, provide a better monitor, remove a compression step when the AVCHD file is created, and synchronization ought to be perfect.
Since my background is audio I feel like I am on thin ice trying to figure out video problems. While the PIX seems like a perfect solution for what I do it also seems expensive and might create a whole new set of problems. My concerns include:
the files from the PIX might be huge since the HDMI from a camera is uncompressed,
would an HDMI feed via HDMI cable be bullet proof in concert situations,
are there any circumstances in manual mode where the camera would display icons in the HDMI output,
I can open MOV files in Vegas (from my Nikon Camera) but wonder how different the files from the PIX might be,
Vegas doesn’t seem to have been designed for MOV, would it create problems over time investing in a device that only creates MOV files?Adding a raid device and upgrading to Vegas Pro seems like good advice. The PIX could improve my output and speed things up if it works well with Vegas and doesn’t create other problems. Any thoughts?
Thanks,
Tom -
3 Replies
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[Tom Yeiser] “The ‘Video Guys’ suggested that the hard drive, over 50% full could be the problem. They suggested adding a raid drive and if that didn’t fix things upgrade to Vegas Pro.”
I’m surprised that the “Video Guys” didn’t tell you that you will NEVER get video and audio recorded in sync on two separate devices unless they are genlocked. It’s simply impossible because each device has it’s own clock crystal which will drift over time from the other devices clock crystal. Genlock will drive both devices from the same clock but it’s not a cheap solution because both devices also need to support genlock. This is usually only found in expensive broadcast equipment.
An alternate solution is actually very simple. Just split the audio every 15 minutes and re-align it on the timeline depending on the drift. You can even stretch it if need but usually I don’t. I shoot long concerts (2 hr+) all the time with my Sony Z1U camera and Marantz PMD-660 and it’s very easy to compensate for the drift in Vegas Pro using this technique.
~jr
http://www.johnrofrano.com
http://www.vasst.com -
Thanks for the reply. Since I am not independently middle class I appreciate a pragmatic solution that does not require another investment.
All AD/DA conversions in my recording studio runs off of a master clock. All outboard gear that have converters sync to word clock, a relatively inexpensive solution in audio. I guess in this case I am only surprised at over such a short period of time that drift becomes significant and how expensive it is to sync video to audio.
Thanks again,
Tom -
So you understand about how important a master clock is. Yea, cameras that support that are expensive. A drift over 15 minutes isn’t that bad. Dave Haynie explains how “The cheap everyday crystals used to drive microprocessors come in at about 100ppm (parts per million), which translates to a loss of sync of one frame at 24fps every 6.9 minutes.” in this post. So 15 minutes is pretty good for a consumer camcorder.
~jr
http://www.johnrofrano.com
http://www.vasst.com
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